Method for producing porous ceramic

ABSTRACT

The present invention relates to a method for producing porous ceramic, the method including molding a mixture containing a water absorbent polymer particle, a ceramic raw material, and water, the water absorbent polymer particle having a water absorption amount in a range of 5 to 30 ml/g at a pressure of 980 Pa, and heating and baking the resulting molded product. The water absorbent polymer particle is preferably composed of a polymer having a 2-acrylamide-2-methylpropanesulfonic acid unit or an acrylamide unit as a constituting monomer unit.

TECHNICAL FIELD

The present invention relates to a method for producing a porous ceramic(i.e., ceramic having many fine pores), and particularly relates to amethod for producing a porous ceramic with high porosity and highstrength. Intended uses of the porous ceramic include filtrationmaterials such as a ceramic filter for cleaning auto exhaust gas, aceramic filter for cleaning exhaust gas exhausted from a thermal engineand a combustion equipment and a ceramic filter for filtering a liquid,such as water, catalytic carriers, such as catalysts for cleaningexhaust gas, heat exchange materials for cleaning automotive exhaustgas, thermal storage media, sintered substrates for batteries, heatinsulating materials, and microbial carriers used for waste waterdisposal.

BACKGROUND ART

As a method for producing a porous ceramic, a method for utilizing a rawmaterial where a ceramic aggregate itself is porous, and a method formixing a foaming agent with a ceramic raw material have been known.There are problems in that in the former method, flexibility of designis less due to restriction of the raw materials whereas in the lattermethod, it is difficult to control properties of a pore amount and apore size with good reproducibility. To solve those problems, a methodhave been known in which a water absorbent polymer which previously hasabsorbed water and has been swollen is used as a pore-forming agent andis added to a ceramic raw material and is kneaded, then the resultingmixture is molded into a certain shape, and subsequently dried or baked(see Japanese Laid-Open Patent Publication Nos. 62-212274, 8-73282,10-167856 and 10-245278).

DISCLOSURE OF THE INVENTION

In the method of mixing the water absorbent polymer which previously hasabsorbed water and been swollen as a pore-forming agent with the ceramicraw material, molding and baking, not only the volume of the polymeritself which has absorbed water and been swollen but also the poremaking action by producing voids between aggregate of the ceramic rawmaterial by the water volume absorbed and retained inside are utilized.

However, in the prior art disclosed in the above-described PatentDocuments, it is difficult to control a pore size distribution of abaked ceramic body and hardness of a kneaded product in steps due to areason that the water absorbent polymer reverses the water beforebaking. It is an object of the present invention to provide a method forproducing a porous ceramic, in which it is easy to control a pore sizedistribution of a baked ceramic body and a hardness of a kneaded productin steps, thereby obtaining a baked ceramic body with high porosity.

In order to solve the above problems, the method for producing theporous ceramic of the invention is characterized by including a step ofmolding a mixture containing water absorbent polymer particles where awater absorption amount is 5 to 30 ml/g at a pressure of 980 Pa, aceramic raw material and water and a step of heating/baking a resultingmolded product.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an apparatus for measuring a water absorption amount undera pressurization condition, in which the follow reference numerals areused.

-   -   1 burette    -   2 pinch cock    -   3 silicone tube    -   4 polytetrafluoroethylene tube    -   5 funnel    -   6 sample (water absorbent polymer particles)    -   7 paper filter for holding sample    -   8 columnar cylinder (made of stainless, having many holes)    -   9 adhesive tape    -   10 paper filter for apparatus    -   11 weight (cylindrical, made of stainless)    -   12 deionized water

BEST MODE FOR CARRYING OUT THE INVENTION

In the specification, the terms “acryl” and “methacryl” are togetherreferred to as (meth)acryl. The terms “acrylate” and “methacrylate” aretogether referred to as (meth)acrylate.

The water absorbent polymer particle used in the present inventionfunctions as a pore-forming agent, and has a water absorption amount ina range of 5 to 30 ml/g at a pressure of 980 Pa. This means that 1 g ofthe water absorbent polymer in a dry state is capable of absorbing 5 to30 ml of deionized water.

If the water absorption amount at a pressure of 980 Pa is less than 5ml/g, it is necessary to add a great amount of pore-forming agent inorder to obtain a sufficient porosity, and thus it is sometimesproblematic in that organic gas is excessively produced when baking,which sometimes goes beyond explosion limit, and a prolonged baking timeis required. On the other hand, if it is greater than 30 ml/g, it may bedifficult to control the hardness of a kneaded product and a bakedproduct. For a reason thereof, it is believed that water contained inthe water absorbent polymer is easily reversed when the mixturecontaining the water absorbent polymer particle, the ceramic rawmaterial and water is kneaded due to a shear force applied to themixture, and that consequently a water-absorbing amount and a particlediameter of the polymer are easily changed. It is also not preferablebecause a large amount of water is required for preparing the kneadedproduct (or argil) with appropriate hardness for molding and an energyamount required for drying a water content is remarkably increased.

When the water absorption amount at a pressure 980 Pa is represented asX ml/g and the water absorption amount at a pressure of 9800 Pa isrepresented as Y ml/g, it is preferable that the water absorbent polymerparticles have a ratio of X/Y in the range of 1.0 to 1.6. When the aboveratio is greater than 1.6, it may be difficult to control the hardnessof the kneaded product and the baked product. For a reason thereof, itis believed that the water contained in the water absorbent polymer iseasily reversed due to the shear force applied to the mixture when themixture containing the water absorbent polymer, the ceramic raw materialand the water is kneaded, and that consequently a water-absorbing rateand a particle diameter of the polymer are easily changed. Normally, theratio is never less than 1.

The water absorbent polymer particle having 30 ml/g or less of the waterabsorption amount at a pressure of 980 Pa also has a relatively highcrosslinking density and a relatively high strength. This is generallyequivalent to that the larger “(osmotic pressure of ions)+(affinity ofmacromolecular electrolyte)” is, that the larger the water absorptionamount is, “the greater the crosslinking density of polymer particlesis, the less the water absorption amount is” and that “the strength ofpolymer particles is increased in proportion to the crosslinking densityof polymer particles”.

The water absorbent polymer particle is preferably spherical in shape inthe state where the particle has absorbed water and has been swollen. Anaverage particle diameter in the saturated water-absorbing state fallspreferably into the range of 1/30 to 1/1, more preferably 1/15 to ½, andstill more preferably 1/15 to ⅓ based on a thickness of a ceramic moldedproduct. When the particle diameter is excessively low, a porosity ofthe resulting ceramic baked product becomes low. For example, when theceramic baked product is used as a filter, a pressured loss of gas orliquid passed through becomes large in some cases. When the particlediameter is excessively large, the strength of the resulting ceramicbaked product becomes insufficient in some cases. The thickness of theceramic molded product means a thickness of an individual wall when theceramic molded product has multiple wall structures composed of theceramic, and does not mean a thickness of a cluster as the entireceramic molded product.

Examples of the water absorbent polymer particles include (1) one wherea polymer obtained by polymerizing a vinyl monomer in an aqueoussolution is dried followed by being pulverized into appropriate sizes,(2) a spherical polymer obtained by inverse suspension polymerization ofa vinyl monomer, (3) a water absorbent polymer obtained by giving amodification treatment such as saponification to spherical hydrophobicpolymer particles obtained by suspension polymerization of a vinylmonomer, and (4) one which makes a modified product of a graft polymercontaining a macromolecular unit composed of starch and a macromolecularunit except for starch as an active ingredient.

Examples of the vinyl monomers which can be used in the above (1) and(2) include water soluble monomers having hydrophilic group, such assulfone group, carboxyl group, amide group, amino group and hydroxylgroup, i.e., 2-acrylamide-2-methylpropanesulfonic acid, 2-(meth)acryloylethanesulfonic acid, styrenesulfonic acid, (meth)acrylic acid, maleicacid, itaconic acid, crotonic acid, fumaric acid and/or partially alkalineutralized products thereof, (meth)acrylamide, N,N-dimethylacrylamide,N-isopropylacrylamide, N-methylol(meth)acrylamide,N-alkoxymethyl(meth)acrylamide, diethylaminoethyl (meth)acrylate,dimethylaminoethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate,N-vinylpyrrolidone, acryloylmorpholine and the like. Such monomers maybe used in mixture with two or more. In terms of easy control ofpolymerization and water-absorbing performance,2-acrylamide-2-methylpropanesulfonic acid,2-(meth)acryloylethanesulfonic acid, (meth)acrylic acid,(meth)acrylamide, N,N-dimethylacrylamide, and N-methylol(meth)acrylamideare preferable, and in particular, 2-acrylamide-2-methylpropanesulfonicacid and acrylamide are preferable.

Examples of the polymer of (3) include a saponified product of acopolymer of vinyl acetate and methyl acrylate. The polymer of (4)includes, for example, modified polymers, such as a starch-(meth)acrylicacid graft resin, a saponified product of a starch-acrylonitrilecopolymer and a saponified product of a starch-acrylamide copolymer.Additionally, a crosslinked body of a modified copolymer made ofisobutylene and maleic acid anhydride may be included. Two or more ofthe water absorbent polymers previously shown may be combined.

Among them, the spherical water absorbent polymer particle synthesizedby the inverse suspension polymerization is the most preferable becauseit has a good miscibility with the ceramic ingredient and a particlediameter and a water absorption rate are easily controlled by selectinga polymerization condition. A shape of a water absorbent polymerparticle affects a shape of a pore of the porous ceramic obtained bybaking. Generally, when the shape of the pore of the baked porousceramic body is spiky, it has been known that stress is concentrated toa tip of a spiky shape to be easily broken and a strength thereofbecomes insufficient. On the contrary, a spherical water absorbentpolymer particle is desirable because the pore becomes spherical andthus a ceramic strength becomes high. When a pulverized article of thewater absorbent polymer is used, it is preferable to uniform theparticle diameter by classifying after the pulverization.

The water absorbent polymer may be a crosslinked one. The crosslinkedwater absorbent polymer has a relatively high strength and thus theshape is unlikely to break up in a step of kneading with ceramic rawmaterials. Therefore, it is easy to obtain the porous ceramic which isexactly the same as a design having the pores with intended shape andsize.

One example of means for introducing a crosslinking structure into thewater absorbent polymer includes simultaneous use of a crosslinkingagent which is a multifunctional vinyl monomer when producing the waterabsorbent polymer. Examples of the multifunctional vinyl monomer used asthe crosslinking agent include di- or tri-(meth)acrylate of polyols,such as polyethyleneglycol di(meth)acrylate, polypropyleneglycoldi(meth)acrylate, glycerin tri(meth)acrylate, and trimethylolpropanetri(meth)acrylate; and bisamides, such as methylenebis(meth)acrylamide.Among them, methylenebisacrylamide and polyethyleneglycol diacrylate areparticularly preferable.

Preferable amount of the multifunctional vinyl monomer to be used is 0.1to 10 mol, more preferably 0.5 to 8 mol, and still more preferably 1.0to 5 mol based on 100 mol of a monofunctional vinyl monomer to be used.That is, molar ratio of the multifunctional vinyl monomer to themonofunctional vinyl monomer is in a range of 0.1:100 to 10:100. If theamount of the multifunctional vinyl monomer is less than 0.1 mol basedon 100 mol of a monofunctional vinyl monomer, an effect to enhance thestrength of the kneaded product with the ceramic raw material can not besufficiently exerted in some cases. If the amount of the multifunctionalvinyl monomer is greater than 10 mol based on 100 mol of amonofunctional vinyl monomer, it is difficult to adjust to a preferablewater-absorbing performance in some cases.

As another example of means for introducing the crosslinking structureinto the water absorbent polymer, there is a method of using acrosslinking agent having a reactivity with a carboxyl group and aneutralized carboxyl group contained in a monomer constituting the waterabsorbent polymer. Examples of said monomer constituting the waterabsorbent polymer include an unsaturated carboxylic acid monomer and apartially neutralized salt of the unsaturated carboxylic acid monomer.Examples of such a crosslinking agent include polyglycidyl compounds,such as (poly)ethyleneglycol diglycidyl ether, (poly)propyleneglycoldiglycidyl ether, (poly)glycerol diglycidyl ether, (poly)glyceroltriglycidyl ether, sorbitol diglycidyl ether, sorbitol triglycidylether, pentaerythritol diglycidyl ether, pentaerythritol triglycidylether and pentaerythritol tetraglycidyl ether; haloepoxy compounds, suchas epichlorohydrin, epibromohydrin and α-methyl-epichlorohydrin; andisocyanate compounds, such as 2,4-tolylene diisocyanate andhexamethylene diisocyanate. Among them, ethyleneglycol diglycidyl etheris particularly preferable.

When a cordierite raw material is used as a ceramic raw material, as thewater absorbent polymer, those which contain no alkali metal and noalkali earth metal are desirable. Because, if the polymer which containsthe above metal abundantly, a cordierite reaction is inhibited to causephysical property reduction, e.g., increase of thermal expansioncoefficient. Therefore, for the water absorbent polymer containingsulfone group and carboxyl group therein, it is desirable that thesefunctional groups do not exist as a sodium salt and a potassium salt andexist in a unneutralized state or as an ammonium salt. Additionally, thewater absorbent polymer containing a nonionic hydrophilic functionalgroup is included as a desirable one. Examples of the nonionichydrophilic functional group include hydroxyl group, oxyalkylene group,such as oxyethylene group and oxypropylene group, amide group, and thelike.

The ceramic raw materials used in the present invention include potteryand porcelain materials, e.g., clay, clay mineral, chamotte, silica,silica sand, diatomaceous earth, pottery stone, feldspar, blast furnaceslag, whitebait, whitebait balloon, fly ash, and in addition, specialceramic raw materials, e.g., cordierite, talc, alumina, kaolin, aluminumhydroxide, magnesia, ferrite, zeolite, mullite, apatite, slag, siliconcarbide, zirconia, aluminum nitride and aluminum titanate, and rawmaterials for electrodes of batteries, e.g., nickel powder, cobaltpowder, lantern manganite, lantern strontium manganite, and the like.

A method for producing the porous ceramic includes kneading and moldinga mixture containing the above ceramic raw material, the water absorbentpolymer particles and water. If necessary, the mixture may furthercontains a binder, such as methyl cellulose, and a lubricant, such asolefin wax. The kneading may be performed according to any knownmethods, and can be performed with using, for example, a kneader, a ponymixer, a screw extruder, a vacuum kneader, or the like. As the ceramicraw material, powder is normally used.

Also, steps of drying and baking the resulting molded product areincluded. The drying and baking may be performed according to any knownmethods. A high-frequency dielectric exothermic heating apparatus, a hotair dryer, a heated bed dryer, a mangle dryer, a tunnel dryer and thelike can be used. Normally, it is preferable to dry at a temperature of150° C. or less until the product does not substantially containmoisture. The baking is performed by heating to a temperature greaterthan 150° C., and preferably to 800° C. or greater. A baking temperatureand a baking time are set so that organic materials, such as the waterabsorbent polymer particles and the binder, are sufficiently burned andthe ceramic raw material is sufficiently baked.

For a ratio of amounts of the ceramic raw material to the waterabsorbent polymer particles to be used, the amount of the waterabsorbent polymer particles is preferably 0.1 to 20 parts by mass, andmore preferably 0.5 to 10 parts by mass based on 100 parts by mass ofthe ceramic raw material in a dry state (containing no water). When theamount of the water absorbent polymer to be used is less than 0.1 partsby mass, a sufficient porosity is not obtained in some cases. When it isgreater than 20 parts by mass, it is sometimes problematic in thatorganic gas is excessively produced at baking, which sometimes goesbeyond an explosion limit, and a baking time is prolonged, a volumechange during the baking is large, and thus the resulting ceramic moldedproduct easily becomes one having distortions and cracks.

The mixture containing the water absorbent polymer particles, theceramic raw material and water is obtained by mixing these raw materialsby arbitrary methods. The amount of water to be used is regulateddepending on types of the water absorbent polymer particles and theceramic raw material and formulation thereof so that preferable hardnessand moldability of the kneaded product are obtained. The amount of 100parts by mass or less of water to be used based on 100 parts by mass ofthe ceramic raw material is preferable because a time required fordrying the kneaded product and energy cost are not excessive.

A method for adding the water absorbent polymer particles in rawmaterial mixing may be either a method for adding a hydrous one (waterabsorbing state) or a method for adding a dried one. An appearance ofthe water absorbent polymer particles in a hydrous state may be a powderor a paste.

When the water absorbent polymer particles in the hydrous state is used,a moisture content ratio thereof is not particularly limited, but it ispreferable to make the moisture ratio capable of handling the waterabsorbent polymer as the powder, i.e., in the range where the waterabsorbent polymer has fluidity. Because, it is difficult to handle thepolymer particles in a gel state due to the high hydrous ratio, mixingand dispersing with the ceramic raw material become insufficient, andthe strength and the porosity of the ceramic molded product after bakingbecome insufficient in some cases.

The water absorbent polymer particles in a dry powder or a powder wherethe hydrous ratio is controlled are easily mixed with the ceramic rawmaterial, and the resulting mixture of the water absorbent polymerparticles and the ceramic raw material has highly uniformdispersibility. That is, a method in which water is added to and mixedwith the powder mixture of the water absorbent polymer particles and theceramic raw material where the powder water absorbent polymer particlesand the powder ceramic raw material have been mixed in advance is apreferable method by which the resulting raw material mixture easilybecomes uniform and in a ceramic molded product obtained by drying andbaking a molded raw material mixture, the strength is high and a poredistribution is uniform. On the other hand, in a method in which thepowder water absorbent polymer particles and the powder ceramic rawmaterial have not been mixed in advance and the water absorbent polymerparticles, the ceramic raw material and water are substantiallysimultaneously mixed, the resulting raw material mixture sometimesbecomes uneven, and in a ceramic molded product obtained by drying andbaking a molded raw material mixture, the strength is insufficient and apore distribution is uneven in some cases.

In the kneading and molding steps, for obtaining good moldability, it isnecessary to make the hardness of the kneaded product fall into anappropriate range. Generally, the hardness of the kneaded product iseasily changed depending on the type of the ceramic raw material, theamount of the water absorbent polymer particles to be added, the watercontent and the kneading method, and the reproducible hardness is notoften obtained even when the method is performed under the samecondition. When the water absorbent polymer particles of the presentinvention are used under the condition once set, the intended hardnessof the kneaded product is easily reproduced, therefore, the steps areeasily controlled and the molding can be stably performed. Any knownmethods can be employed for other conditions.

EXAMPLES Preparation Example 1 Production of Water Absorbent PolymerParticles A to E by Inverse Suspension Polymerization

In a 3 liter separable flask, 1603 g of n-hexane and 10 g of sorbitanmonolaurate (HLB 4.3) were placed and dissolved. Meanwhile, 96 g ofacrylic acid, 224 g of 2-acrylamide-2-methylpropanesulfonic acid, and14.9 g of methylene bisacrylamide (crosslinking agent; amount of thecrosslinking agent is 4 mol based on 100 mol of monomers except for thecrosslinking agent) were dissolved in 286.4 g of deionized water, and124.67 g of an aqueous solution of 25% ammonia was added withice-cooling to prepare a partially neutralized (75 mol % neutralized)monomer aqueous solution.

The monomer aqueous solution was added with stirring the content in theseparable flask at 400 rpm (rotation/min), and nitrogen substitution wasperformed at a flow rate of 200 ml/min for 2 hours until a dissolvedoxygen concentration became sufficiently low. An external temperaturewas controlled at 30° C., and when the temperature of the content in theflask became stable, 0.58 g of an aqueous solution of 6.9%t-butylhydroperoxide was added. Then, 0.90 g of an aqueous solution of5% sodium bisulfite was added in five portions, and in which one portionwas added to initiate polymerization. A temperature elevation in areaction solution due to polymerization heat was observed. When thetemperature of the reaction solution was lowered to the temperaturewhich was nearly equal to the external temperature controlled at 30° C.,one portion of the remaining 4 portions of the sodium bisulfite aqueoussolution was added. A procedure where when the temperature was onceelevated and then lowered to the temperature nearly equal to theexternal temperature, one portion of the sodium bisulfite aqueoussolution was added was further repeated three times. After adding thefifth portion of the sodium bisulfite aqueous solution, when the onceelevated temperature was lowered to the temperature nearly equal to theexternal temperature, the reaction solution was matured as it was forone hour. After the initiation of the polymerization, the externaltemperature was also controlled at 30° C., the nitrogen substitution wascontinued, and the stir at 400 rpm was continued until the completion ofthe reaction. After separating two phases by leaving to stand, asupernatant was discarded. Thereafter, a precipitate in a lower layerwas dried at 120° C. for 6 hours, and pulverized by a pulverizer toyield spherical water absorbent polymer particles A.

The water absorbent polymer particles B and C were produced in thesimilar preparation condition for the water absorbent polymer particleA, except for changing the amount of methylenebisacrylamide to be addedbased on 100 mol of monomers except for the crosslinking agent to 3 moland 2 mol, respectively.

The water absorbent polymer particle D was produced in the similarpreparation condition for the water absorbent polymer particle A, exceptfor changing the monomers except for the crosslinking agent to 224 g of2-acrylamide-2-methylpropanesulfonic acid and 192 g of an aqueoussolution of 50% acrylamide, and changing the amounts of 25% ammoniaaqueous solution and the deionized water to 55.1 g and 261.8 g,respectively.

It was the similar preparation condition to that for the water absorbentpolymer particle A that amount of methylenebisacrylamide, which servesas the crosslinking agent, was 4 mol based on 100 mol of the monomersexcept for the crosslinking agent.

The water absorbent polymer particle E was produced as was the case withthe water absorbent polymer particle A, except for changing the monomersexcept for the crosslinking agent to 480 g of an aqueous solution of 50%acrylamide and 80.0 g of acrylic acid, and changing the amounts of 25%ammonia aqueous solution and the deionized water to 56.6 g and 114.7 g,respectively.

It was also the same condition as that for the water absorbent polymerparticle A that amount of methylenebisacrylamide, a crosslinking agent,was 4 mol based on 100 mol of the monomers except for the crosslinkingagent.

All of the water absorbent polymer particles B to E had a sphericalshape.

Preparation Example 2 Production of Water Absorbent Polymer Particles Fand G

An aqueous solution of 35% by mass of acrylic acid was prepared bymixing 100 g of acrylic acid and deionized water and then adding anaqueous solution of 25% ammonia to partially neutralize (75 mol %neutralization) with ice-cooling, and 20 g of Aronix M-245(polyethyleneglycol diacrylate, repeat units of oxyethylene: about 9)supplied from Toagosei Co., Ltd. was added as the crosslinking agent. Asphotoinitiators, 0.01 g of 2,2-dimethoxy-2-phenylacetophenone and 0.1 gof ammonium persulfate were added to this monomer solution, which wasthen placed in a cylindrical glass vessel (reaction vessel) with aninner diameter of 146 mm, and nitrogen bubbling was performed for 30minutes with keeping the temperature of the aqueous solution at 20° C.Thereafter, ultraviolet light at a dose of 5.0 mW/cm² was irradiated for3 minutes from the above portion of the reaction vessel using a 100 Wblack light (product name: H100BL, supplied from Toshiba Corporation) tomake a sheet hydrous crosslinked polymer gel (accumulated lightintensity: 900 mJ/cm²). This gel was dried and pulverized to affordcrude particles of a water absorbent resin. Then, the crude particleswere pulverized in a ball mill and those which passed through a sievewith 330 mesh (45 μm) were collected to yield the water absorbentpolymer particles F.

The water absorbent polymer particle G was produced in the similarpreparation condition for the water absorbent polymer particle F, exceptthat 200 g of an aqueous solution of 50% acrylamide and deionized waterwere mixed to prepare the aqueous solution of 30% by mass of acrylamide,and 10 g of Aronix M-240 (polyethyleneglycol diacrylate, repeat units ofoxyethylene: about 4) supplied from Toagosei Co., Ltd. was added as thecrosslinking agent.

<Measurement of Water Absorption Amount Under Pressurization of WaterAbsorbent Polymer Particles>

A water absorption amount under pressurization of water absorbentpolymer particles, i.e., the water absorption amount at a pressure of980 Pa or 9800 Pa was measured using a measurement apparatus shown inFIG. 1. As is shown in FIG. 1, the measurement apparatus is composed ofunits (1) to (3). The unit (1) includes a burette 1 with a branch ductfor air vent, a pinch cock 2, a silicone tube 3 and apolytetrafluoroethylene tube 4. In the unit (2), a columnar cylinder 8having many holes at its bottom is placed on a funnel 5, and paperfilter 10 for the apparatus is further placed thereon. As shown in theunit (3), a sample 6 of the water absorbent polymer particles issandwiched between two sheets of paper filter 7 for holding the sample,which is then fixed to a cylindrical weight 11 by an adhesive tape 9.There are two types of cylindrical weights, and a load of 980 Pa or 9800Pa is applied to the sample 6. The units (1) and (2) are communicatedwith a silicone tube 3. Heights of the funnel 5 and the columnarcylinder 8 are fixed with respect to the burette 1, and set so that thelevel of the lower end of polytetrafluoroethylene tube 4 placed in theburette branch duct and the level of the bottom of the columnar cylinder8 are the same (dot line in FIG. 1).

The water absorption amount under pressurization was measured using themeasurement apparatus of the above configuration. The measurement methodwill be illustrated below. The pinch cock 2 in the unit (1) was removed,deionized water was placed from the above portion of the burette 1through the silicone tube 3, and the space from the burette 1 to thepaper filter 10 in the apparatus was filled with the deionized water.Then, the pinch cock 2 was closed to retain the pressure inside theburette 1, and the air was removed from the polytetrafluoroethylene tube4 connected to the burette branch duct through a rubber plug. Thus, thedeionized water was continuously supplied from the burette 1 to thepaper filter 10 for the apparatus. Then, excess deionized water whichhas bled from the paper filter 10 for the apparatus was eliminated, andsubsequently a scale (a) of the burette 1 was read and recorded. Then,0.05 g of the water absorbent polymer particle sample was weighed,evenly placed on a center portion of the paper filter 7 for holding thesample as shown in the unit (3), sandwiched the dry water absorbentpolymer particle sample with another paper filter, and secured at thebottom of the cylindrical weight 11 by the adhesive tape 9. The weight11 to which the sample was secured was placed on the paper filter 10 forthe apparatus shown in the unit (2). Then, 30 minutes after placing theweight 11 on the paper filter 10 for the apparatus, a scale (b) of theburette 1 was read and recorded. The sum of the water absorption amounts(c) of the water absorbent polymer particles and two sheets of paperfilter 7 is obtained from the expression of (a-b). By the sameprocedure, the absorption amount of two sheets of paper filter 7 whichcontained no water absorbent polymer particle was measured (d). Thewater absorption amount under pressurization was obtained from thefollowing formula.Water absorption amount under pressurization (ml/g)=(c-d)/(weight ofwater absorbent polymer particles (g))

As in the above, the water absorption amounts were measured for eachsample with loads of 980 Pa and 9800 Pa.

<Measurement of Kneaded Product Hardness>

The hardness of the kneaded products (before molding/baking) obtained inExamples and Comparative Examples was measured by the method shownbelow. The kneaded product was tightly soaked in a 50 ml screw vial suchthat no space may be provided, and the surface was flattened. Thiskneaded product was retained at 23° C., and the hardness thereof wasmeasured using a card meter (ME-303, Iio Denki) under the followingconditions:

Load: 400 g;

Diameter of the pressure sensitive shaft: 3 mm φ; and

Fall velocity of the pressure sensitive shaft: 0.36 cm/sec.

The hardness of the kneaded product which had favorable moldability inthe conditions used in Examples and Comparative Examples was in therange of 1.5×10⁴ to 6.0×10⁴ N/m².

<Evaluation of Moldability>

The appearance of the molded product (before baking) obtained by moldingthe kneaded product cylindrically by an extrusion molding method wasvisually evaluated. Those which had crack(s) or could not keep acylindrical shape when left to stand were indicated by X (poor shaperetention), and those which had no crack and were good in shaperetention were indicated by o.

Example 1

The polymer particles A produced in Preparation example 1 were used asthe water absorbent polymer particles. The water absorption amount ofthe polymer particles A at a pressure of 980 Pa was 9 ml/g, an X/Y ratiowhen the water absorption amount at a pressure of 980 Pa was X ml/g andthe water absorption amount at a pressure of 9800 Pa was Y ml/g was1.32, the water absorption amount at an ambient pressure (mass(including the mass of the polymer itself) represented by g unit when 1g of the water absorbent polymer in a dry state absorbed and saturateddeionized water at an ambient pressure) was 10 g/g, and an averageparticle diameter at a water-absorbing and saturated state was 40 μm.The water absorption amount of the polymer particles A at an ambientpressure means the water absorption amount measured with slightlypressing without using the “weight 11” in the above “Measurement ofwater absorption amount under pressurization of water absorbent polymerparticles”. The water absorption amount of the polymer particles B, Cand D at an ambient pressure is the same as this.

As the ceramic raw material, kaolin, calcined kaolin, talc, alumina,aluminum hydroxide and silica, which are cordierite materials, wereformulated at a mass ratio of 21:13:39:9:13:5 (total 100 parts by mass).Thereto, 4 parts by mass of methyl cellulose which was a binder, 1 partby mass of olefin wax which was a lubricant and 5 parts by mass of thewater absorbent polymer particles A which was a pore making agent wereadded and mixed, subsequently 80 parts by mass of deionized water wasadded, and immediately kneaded by an σ-type kneader for 30 minutes.Subsequently, the kneaded product was molded cylindrically by anextrusion molding method, and water was eliminated by drying. The dryingwas performed at 120° C. until the weight almost became constant. Then,the temperature was raised to 1000° C., then the temperature was raisedat a temperature rising rate of 50° C./hour from 1000° C. to 1400° C.,and after the temperature reached 1420° C., it was retained to bake for4 hours. A porosity of the baked body was measured by a mercuryporosimeter.

Example 2

Example 2 was performed similarly to procedures of Example 1 except thatthe amount of deionized water was changed from 80 parts by mass to 90parts by mass.

Example 3

Example 3 was performed similarly to procedures of Example 1 except thatthe amount of the water absorbent polymer particles A to be used waschanged from 5 parts by mass to 3.1 parts by mass.

Example 4

Example 4 was performed similarly to procedures of Example 1 except forusing the water absorbent polymer particles B produced in Preparationexample 1 in place of the water absorbent polymer particles A. The waterabsorption amount at a pressure of 980 Pa of the polymer particles B was13 ml/g, the X/Y ratio was 1.33, the water absorption amount at anambient pressure was 15 g/g, and the average particle diameter at awater-absorbing and saturated state was 53 μm.

Example 5

Example 5 was performed similarly to procedures of Example 1 except forusing the water absorbent polymer particles C produced in Preparationexample 1 in place of the water absorbent polymer particles A. The waterabsorption amount at a pressure of 980 Pa of the polymer particles C was20 ml/g, the X/Y ratio was 1.45, the water absorption amount at anambient pressure was 23 g/g, and the average particle diameter at awater-absorbing and saturated state was 62 μm.

Example 6

Example 6 was performed similarly to procedures of Example 1 except forusing the water absorbent polymer particles D produced in Preparationexample 1 in place of the water absorbent polymer particles A. The waterabsorption amount at a pressure of 980 Pa of the polymer particles D was11 ml/g, the X/Y ratio was 1.13, the water absorption amount at anambient pressure was 13 g/g, and the average particle diameter at awater-absorbing and saturated state was 49 μm.

Example 7

Example 7 was performed similarly to procedures of Example 1 except forusing the water absorbent polymer particles E produced in Preparationexample 1 in place of the water absorbent polymer particles A. The waterabsorption amount at a pressure of 980 Pa of the polymer particles E was10 ml/g, the X/Y ratio was 1.36, the water absorption amount at anambient pressure was 12 g/g, and the average particle diameter at awater-absorbing and saturated state was 65 μm.

Example 8

Example 8 was performed similarly to procedures of Example 1 except forusing the water absorbent polymer particles F produced in Preparationexample 2 in place of the water absorbent polymer particles A. The waterabsorption amount at a pressure of 980 Pa of the polymer particles F was27 ml/g, the X/Y ratio was 1.16, the water absorption amount at anambient pressure was 29 g/g, and the average particle diameter at awater-absorbing and saturated state was 42 μm.

Example 9

Example 9 was performed similarly to procedures of Example 1 except forusing the water absorbent polymer particles G produced in Preparationexample 2 in place of the water absorbent polymer particles A. The waterabsorption amount at a pressure of 980 Pa of the polymer particles G was19 ml/g, the X/Y ratio was 1.05, the water absorption amount at anambient pressure was 22 g/g, and the average particle diameter at awater-absorbing and saturated state was 41 μm.

Example 10

Example 10 was performed similarly to procedures of Example 1 except forusing the water absorbent polymer particles H (KI gel 201K, 330 meshpass article supplied from Kuraray Isoprene Chemical Co., Ltd.,pulverized article of salt of crosslinked body of modifiedisobutylene-maleic anhydride copolymer) in place of the water absorbentpolymer particles A. The water absorption amount at a pressure of 980 Paof the polymer particles H was 25 ml/g, the X/Y ratio was 1.32, thewater absorption amount at an ambient pressure was 32 g/g, and theaverage particle diameter at a water-absorbing and saturated state was60 μm.

Comparative Example 1

The same procedures as those in Example 1 were performed except forusing 5 parts by mass of the water absorbent polymer particles I (KI gel201K, granulated article supplied from Kuraray Isoprene Chemical Co.,Ltd., salt of crosslinked body of modified isobutylene-maleic acidanhydrate copolymer) which were not pulverized in place of 5 parts bymass of the water absorbent polymer particles A. The water absorptionamount at a pressure of 980 Pa of the polymer particles I was 35 ml/g,the X/Y ratio was 1.54, the water absorption amount at an ambientpressure was 200 g/g (value on the catalogue), and the average particlediameter at a water-absorbing and saturated state was 320 μm. Themolding of the kneaded product was attempted, but the kneaded productwas not successfully molded due to insufficient fluidity, and crackswere observed on the molded product.

Separately, when the amount of water to be added required for impartingan appropriate fluidity to this kneaded product was searched, it wasfound that 120 parts by mass of water was required. When the water atsuch a large amount was used, more time and energy were required and itwas not practical.

Comparative Example 2

The same procedures as those in Example 1 were performed except forusing 0.15 parts by mass of the water absorbent polymer particles I inplace of 5 parts by mass of the water absorbent polymer particles A. Theresulting kneaded product was poor in shape retention, and the moldedproduct could not keep the shape.

Comparative Example 3

The same procedures as those in Example 1 were performed except forusing 2 parts by mass of the water absorbent polymer particles I inplace of 5 parts by mass of the water absorbent polymer particles A.

Comparative Example 4

The same procedures as those in Example 1 were performed except forusing 5 parts by mass of the water absorbent polymer particles J(pulverized article of Sanfresh ST-500D supplied from Sanyo ChemicalIndustries Ltd., polyacrylic crosslinked resin) in place of 5 parts bymass of the water absorbent polymer particles A. The water absorptionamount at a pressure of 980 Pa of the polymer particles J was 75 ml/g,the X/Y ratio was 1.09, the water absorption amount at an ambientpressure was 400 g/g (value on the catalog), and the average particlediameter at a water-absorbing and saturated state was 190 μm. Themolding of the kneaded product was attempted, but the kneaded productwas not successfully molded due to insufficient fluidity, and crackswere observed on the molded product.

Separately, when the amount of water to be added required for impartingan appropriate fluidity to this kneaded product was searched, it wasfound that 140 parts by mass of water was required. When the water atsuch a large amount was used, more time and energy were required and itwas not practical.

Comparative Example 5

The same procedures as those in Example 1 were performed except forusing 0.08 parts by mass of the water absorbent polymer particles J inplace of 5 parts by mass of the water absorbent polymer particles A. Theresulting kneaded product was poor in shape retention, and the moldedproduct could not keep the shape.

Comparative Example 6

The same procedures as those in Example 1 were performed except forusing 2 parts by mass of the water absorbent polymer particles J inplace of 5 parts by mass of the water absorbent polymer particles A.

Comparative Example 7

The same procedures as those in Example 1 were performed except forusing 5 parts by mass of the spherical water absorbent polymer particlesK (Aqua Keep SA-60N supplied from Sumitomo Seika Chemicals Co., Ltd.,polyacrylamide crosslinked resin) in place of 5 parts by mass of thewater absorbent polymer particles A. The water absorption amount at apressure of 980 Pa of the polymer particles K was 140 ml/g, the X/Yratio was 1.93, the water absorption amount at an ambient pressure was430 g/g, and the average particle diameter at a water-absorbing andsaturated state was 710 μm. The molding of the kneaded product wasattempted, but the kneaded product was not successfully molded due toinsufficient fluidity, and cracks were observed on the molded product.

Separately, when the amount of water to be added required for impartingan appropriate fluidity to this kneaded product was searched, it wasfound that 150 parts by mass of water was required. When the water atsuch a large amount was used, more time and energy were required and itwas not practical.

Comparative Example 8

The same procedures as those in Example 1 were performed except forusing 0.06 parts by mass of the water absorbent polymer particles K inplace of 5 parts by mass of the water absorbent polymer particles A. Theresulting kneaded product was poor in shape retention, and the moldedproduct could not keep the shape.

Comparative Example 9

The same procedures as those in Example 1 were performed except forusing 2 parts by mass of the water absorbent polymer particles K inplace of 5 parts by mass of the water absorbent polymer particles A.

Comparative Example 10

The same procedures as those in Example 1 were performed except forusing 5 parts by mass of the spherical water absorbent polymer particlesL (Aron zap TS-U-1 supplied from Toagosei Co., Ltd., crosslinked polymerhaving acrylic acid units and 2-acrylamide-2-methylpropanesulfonic acidunits) in place of 5 parts by mass of the water absorbent polymerparticles A. The water absorption amount at a pressure of 980 Pa of thepolymer particles L was 98 ml/g, the X/Y ratio was 2.80, the waterabsorption amount at an ambient pressure was 150 g/g, and the averageparticle diameter at a water-absorbing and saturated state was 450 μm.The molding of the kneaded product was attempted, but the kneadedproduct was not successfully molded due to insufficient fluidity, andcracks were observed on the molded product.

Separately, when the amount of water to be added required for impartingan appropriate fluidity to this kneaded product was searched, it wasfound that 120 parts by mass of water was required. When the water atsuch a large amount was used, more time and energy were required and itwas not practical.

Comparative Example 11

The same procedures as those in Example 1 was performed except for using0.2 parts by mass of the water absorbent polymer particles L in place of5 parts by mass of the water absorbent polymer particles A. Theresulting kneaded product was poor in shape retention, and the moldedproduct could not keep the shape.

Comparative Example 12

The same procedures as those in Example 1 were performed except forusing 2 parts by mass of the water absorbent polymer particles L inplace of 5 parts by mass of the water absorbent polymer particles A.

Comparative Example 13

The same procedures as those in Example 1 were performed except forusing 5 parts by mass of the spherical water absorbent polymer particlesM (Aron zap U supplied from Toagosei Co., Ltd., crosslinked polymerhaving an acrylic acid unit as a major structural unit) in place of 5parts by mass of the water absorbent polymer particles A. The waterabsorption amount at a pressure of 980 Pa of the polymer particles M was112 ml/g, the X/Y ratio was 1.67, the water absorption amount at anambient pressure was 210 g/g, and the average particle diameter at awater-absorbing and saturated state was 590 μm. The molding of thekneaded product was attempted, but the kneaded product was notsuccessfully molded due to insufficient fluidity, and cracks wereobserved on the molded product.

Separately, when the amount of water to be added required for impartingan appropriate fluidity to this kneaded product was searched, it wasfound that 120 parts by mass of water was required. When the water atsuch a large amount was used, more time and energy were required and itwas not practical.

Comparative Example 14

The same procedures as those in Example 1 were performed except forusing 0.14 parts by mass of the water absorbent polymer particles M inplace of 5 parts by mass of the water absorbent polymer particles A. Theresulting kneaded product was poor in shape retention, and the moldedproduct could not keep the shape.

Comparative Example 15

The same procedures as those in Example 1 were performed except forusing 2 parts by mass of the water absorbent polymer particles M inplace of 5 parts by mass of the water absorbent polymer particles A.

Data for the hardness of the kneaded products, evaluation results of themoldability and the porosity of the baked bodies in Examples andComparative Examples are shown in Table 1.

TABLE 1 Water absorbent polymer particle water water absorptionabsorption amount at av. diameter Baked amount at ambient of water WaterKneaded product product 980 Pa X/Y pressure saturated amount amounthardness porosity type (ml/g) ratio (g/g) particle (μm) (parts) (parts)(N/m²) moldability (%) Examples 1 A 9 1.32 10 40 5.0 80 5.2 × 10⁴ ◯ 60 2A 9 1.32 10 40 5.0 80 4.5 × 10⁴ ◯ 62 3 A 9 1.32 10 40 3.1 80 4.2 × 10⁴ ◯58 4 B 13 1.33 15 53 5.0 80 5.3 × 10⁴ ◯ 62 5 C 20 1.45 23 62 5.0 80 5.4× 10⁴ ◯ 65 6 D 11 1.13 13 49 5.0 80 5.4 × 10⁴ ◯ 61 7 E 10 1.36 12 65 5.080 5.3 × 10⁴ ◯ 65 8 F 27 1.16 29 42 5.0 80 5.6 × 10⁴ ◯ 58 9 G 19 1.05 2241 5.0 80 5.1 × 10⁴ ◯ 59 10 H 25 1.32 32 60 5.0 80 5.2 × 10⁴ ◯ 59Comparative 1 I 35 1.54 200 320 5.0 80 9.3 × 10⁴ X (cracked) — Examples2 I 35 1.54 200 320 0.15 80 0.4 × 10⁴ X (poor shape retention) — 3 I 351.54 200 320 2.0 80 3.2 × 10⁴ ◯ 54 4 J 75 1.09 400 190 5.0 80 9.2 × 10⁴X (cracked) — 5 J 75 1.09 400 190 0.08 80 0.2 × 10⁴ X (poor shaperetention) — 6 J 75 1.09 400 190 2.0 80 2.4 × 10⁴ ◯ 52 7 K 140 1.93 480710 5.0 80 8.7 × 10⁴ X (cracked) — 8 K 140 1.93 480 710 0.06 80 0.1 ×10⁴ X (poor shape retention) — 9 K 140 1.93 480 710 2.0 80 2.0 × 10⁴ ◯46 10 L 98 2.80 150 450 5.0 80 8.9 × 10⁴ X (cracked) — 11 L 98 2.80 150450 0.20 80 0.3 × 10⁴ X (poor shape retention) — 12 L 98 2.80 150 4502.0 80 3.0 × 10⁴ ◯ 48 13 M 112 1.67 210 590 5.0 80 8.6 × 10⁴ X (cracked)— 14 M 112 1.67 210 590 0.14 80 0.2 × 10⁴ X (poor shape retention) — 15M 112 1.67 210 590 2.0 80 2.1 × 10⁴ ◯ 49

In Comparative Examples 1, 4, 7, 10 and 13, the same amount of the waterabsorbent polymer particles as that in Examples 1, 2, 4, 5, 6, 7, 8, 9and 10 was used, and consequently the moldability of the kneaded productwas poor and the molded product had a crack(s).

It can be speculated that considerable difference in the waterabsorption amounts under an ambient pressure of the known waterabsorbent polymer particles used in Comparative Examples and the waterabsorbent polymer particles used in Examples within the technical scopeof the present invention may affect the above results. Thus, in Example3, and Comparative Examples 2, 5, 8, 11 and 14, the experiments wereperformed using the amount where 30 parts by mass of deionized watercalculated by subtracting 50 parts by mass required for kneading theceramic raw material in the absence of the water absorbent polymer from80 parts by mass which is the total deionized water amount to be usedcorresponded to the saturated water absorption amount. Consequently, inExample 3, the kneaded product had an appropriate hardness and the goodmoldability, but in Comparative Examples 2, 5, 8, 11 and 14, thehardness of the kneaded product was low and the moldability (shaperetention) was poor.

Thus, in Comparative Examples 3, 6, 9, 12 and 15, the amount of thewater absorbent polymer particles to be used was adjusted to 2 parts bymass. Consequently, the condition having the hardness of the kneadedproduct and moldability required was found, but the porosity of theresulting baked product was 46 to 54%, which was less than that inExamples.

Meanings of requirements which characterize the present inventiondescribed in claims will be complemented. The essence of the presentinvention is the use of the water absorbent polymer particles whosewater absorption amount is relatively low (but is not zero) at aroundambient pressure as the pore making agent (invention according to claim1). When the water absorption amount of the water absorbent polymerparticles is excessively low at around ambient pressure, the sufficientporosity is not obtained because the water amount which the polymerparticles retain is low. When the water absorption amount of the waterabsorbent polymer particles is excessively large at around ambientpressure, it may be difficult to control hardness and pore distributionof the kneaded product and the baked product because the water reversesfrom the polymer particles to change the particle diameters when shearforce is applied in the kneading step. However, the water absorptionamount at ambient pressure is greatly affected by the measurementcondition, and additionally when the particle diameters of the waterabsorbent polymer are too small, it is not easy to measure them andreproducibility of the obtained data for the water absorption amount issometimes poor. Thus, in claim 1 of the present invention, the waterabsorption amount at a pressure of 980 Pa obtained by adding a slightload to the ambient pressure is defined as the good condition whichtypifies the ambient pressure (close to the ambient pressure) and inwhich the reproducibility is good.

In claim 2 of the present invention, it is defined that the waterabsorption amount when shear force is applied in the kneading step isnot extremely low compared to the water absorption amount at aroundambient pressure. When the water absorption amount at a pressure of 9800Pa (corresponding to the shear force at kneading) is extremely lowcompared to the water absorption amount at a pressure of 980 Pa(approximating to the water absorption amount at around ambientpressure), the water reverses from the polymer particles to easilychange the particle diameters which have absorbed the water when theshear force is applied in the kneading step, and thus, it may bedifficult to control the kneaded product, the hardness thereof and thepore distribution.

In the aforementioned Japanese Laid-Open Patent Publication No.10-167856, deformation of water absorbent gel was inhibited by makingfine particles of the water absorbent resin with high gel strengthabsorb water and be saturated with water and by the use thereof as thepore making agent. However, the gel strength is for a water absorbentpolymer gel containing saline whose water absorbability is considerablylow compared to purified water, and when used by absorbing the deionizedwater, the reverse of water occurs, i.e., the water absorbent polymerhaving a relatively high water absorption amount is used. In paragraph0012 of Japanese Laid-Open Patent Publication No. 10-167856, it isdescribed that “an absorption performance for purified water is 50 g/gor greater, and preferably 100 to 1000 g/g”. It is shown that it is thetechnique to use the water absorbent resin whose water absorption amountis larger than that of the water absorbent polymer particles suitablyusable for the present invention. In Comparative Examples 4 to 6 of thepresent invention, the water absorbent polymer particles which appearedto be equivalent or similar to the water absorbent polymer used inExample in Japanese Laid-Open Patent Publication No. 10-167856 wereused. In these Comparative Examples, the moldability was poor and theporosity was lower than that in Examples of the present invention.

In the method of suppressing the water absorption amount using saline,it is problematic in that the resulting baked porous ceramic bodycontains a salt in a large amount.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to easily control thehardness and the pore distribution of the kneaded product with ceramicraw material and to provide a porous ceramic with high hardness and highporosity, by using the hard water absorbent resin where the waterreverse due to a shear force caused by kneading unlikely occurs.

Intended uses of such a porous ceramic include filtration materials suchas a ceramic filter for cleaning auto exhaust gas, a ceramic filter forcleaning exhaust gas exhausted from a thermal engine and a combustionequipment and a ceramic filter for filtering a liquid such as water,catalytic carriers such as catalysts for cleaning exhaust gas, heatexchange materials for cleaning automotive exhaust gas, thermal storagemedia, sintered substrates for batteries, heat insulating materials, andmicrobial carriers used for waste water disposal.

1. A method for producing porous ceramic, the method comprising: mixingdry water absorbent polymer particle powder and dry ceramic raw materialpowder to prepare a dry powder mixture, the dry ceramic raw materialpowder being without additional water prior to being mixed with water;mixing the dry powder mixture with water to prepare wet powder mixture,wherein the wet powder mixture contains water absorbent polymerparticles, the ceramic raw material, and the water; molding the wetpowder mixture containing the water absorbent polymer particle powder,the ceramic raw material, and the water, the water absorbent polymerparticles having a water absorption amount in a range of 5 to 30 ml/g ata pressure of 980 Pa, wherein the water absorbent polymer particles,when swollen, have an average diameter 65 micrometers or less; andheating and baking the resulting molded product.
 2. The method forproducing porous ceramic according to claim 1, wherein the waterabsorbent polymer particles have an X/Y ratio in a range of 1.0 to 1.6,wherein X represents the water absorption amount, ml/g, at a pressure of980 Pa and Y represents the water absorption amount, ml/g, at a pressureof 9800 Pa.
 3. The method for producing porous ceramic according toclaim 1, wherein the water absorbent polymer particles are composed of apolymer obtained by radical polymerization of a monomer mixturecontaining a monofunctional vinyl monomer having one unsaturated bondand a multifunctional vinyl monomer having two or more unsaturatedbonds, amount of the multifunctional vinyl monomer being in a range of0.1 mol to 10 mol based on 100 mol of the monofunctional vinyl monomer.4. The method for producing porous ceramic according to claim 1, whereinthe water absorbent polymer particles are composed of a polymer obtainedby polymerizing a vinyl monomer by inverse suspension polymerization. 5.The method for producing porous ceramic according to claim 1, whereinthe water absorbent polymer particles are composed of a polymer having a2-acrylamide-2-methylpropanesulfonic acid unit or an acrylamide unit asa constituting monomer unit.
 6. The method for producing porous ceramicaccording to claim 1, wherein the water absorbent polymer comprises acrosslinking agent such that the water absorbent polymer particles havea crosslinked structure when the mixture is kneaded.
 7. A method forproducing porous ceramic, the method comprising: mixing dry waterabsorbent polymer particle powder and dry ceramic raw material powder toprepare a dry powder mixture, the dry ceramic raw material powder beingwithout additional water prior to being mixed with water; mixing the drypowder mixture with water to prepare wet powder mixture, wherein the wetpowder mixture contains water absorbent polymer particles, the ceramicraw material, and the water; molding the wet powder mixture containingthe water absorbent polymer particle powder, the ceramic raw material,and the water, the water absorbent polymer particles having a waterabsorption amount in a range of 10 to 32 g/g or 5 to 30 ml/g at apressure of 980 Pa; and heating and baking the resulting molded product.8. The method of claim 7, wherein the water absorbent polymer particleshave an X/Y ratio in a range of 1.0 to 1.6, wherein X represents thewater absorption amount, ml/g, at a pressure of 980 Pa and Y representsthe water absorption amount, ml/g, at a pressure of 9800 Pa.
 9. Themethod of claim 7, wherein the water absorbent polymer particles, whenswollen, have an average diameter 65 micrometers or less.
 10. The methodof claim 7, wherein the water absorbent polymer comprises a crosslinkingagent such that the water absorbent polymer particles have a crosslinkedstructure when the wet powder mixture is kneaded.
 11. A method forproducing porous ceramic, the method comprising: mixing a dry waterabsorbent polymer powder and ceramic raw material powder to prepare adry powder mixture, the dry water absorbent polymer particle powderbeing without additional water prior to being mixed with water andhaving a water absorption amount in a range of 5 to 30 ml/g at apressure of 980 Pa; mixing the powder mixture with water to prepare wetpowder mixture, wherein the wet powder mixture is said mixturecontaining a water absorbent polymer particle, a ceramic raw material,and water; molding the mixture, wherein the water absorbent polymerparticle; and heating and baking the resulting molded product.
 12. Themethod of claim 11, wherein the ceramic raw material powder is a dryceramic raw material powder being without additional water prior tobeing mixed with water.
 13. The method of claim 11, wherein the waterabsorbent polymer particle has an X/Y ratio in a range of 1.0 to 1.6,wherein X represents the water absorption amount, ml/g, at a pressure of980 Pa and Y represents the water absorption amount, ml/g, at a pressureof 9800 Pa.
 14. The method of claim 11, wherein the water absorbentpolymer particle, when swollen, has an average diameter 65 micrometersor less.
 15. The method of claim 11, wherein the water absorbent polymercomprises a crosslinking agent such that the water absorbent polymerparticle has a crosslinked structure when the mixture is kneaded.